Tuesday, March 19, 2013

by Lincoln Park Zoo

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Nature Boardwalk

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Zoo scientists are building specialty nest boxes to encourage black-capped chickadees to nest at Nature Boardwalk at Lincoln Park Zoo.

It’s been almost three years since the creation of Nature Boardwalk at Lincoln Park. The native plant community has become well established, creating natural habitat for many different species right here in the heart of Chicago.

Last year zoo biologists noted an increase in native birds nesting around the boardwalk. Red-winged blackbirds nested en masse in the bulrush surrounding the pond, and Baltimore orioles and house finches used the oak trees next to the People’s Gas Education Pavilion.

All this nesting represents a great success for Nature Boardwalk. However, one group remains conspicuously absent from the boardwalk during breeding season: cavity-nesting birds.

What Is a Cavity-Nesting Bird?
Cavity-nesting birds nest in chambers inside trees. Woodpeckers, eastern bluebirds and nuthatches are all examples of this group. There are more than 80 different cavity-nesting bird species in North America. Of these, some excavate their own cavity to nest in while others use old excavated cavities or find tree cavities caused by natural decay. Tree cavities don’t just play a critical role for these bird species; many mammals, including bats, also use this habitat to roost.

In natural areas, cavity-nesting birds commonly use standing dead trees (snags) for nesting, perching and foraging. Snags are commonly removed in urban areas for safety concerns or aesthetic reasons, though, causing a decline in the number of cavity-nesting sites available.

Making matters worse, cavity-nesting birds often have to compete with urban invasive species with higher population densities. For example, the house sparrow is one of the most abundant invasive species in urban areas due to its ability to adapt to a human-modified landscape. These birds are a significant competitor for local cavities.

To try to help our cavity-challenged friends, Lincoln Park Zoo’s Urban Wildlife Institute has set out to encourage one particular local species to nest at Nature Boardwalk: black-capped chickadees.

Bringing Chickadees to Nature Boardwalk
Black-capped chickadees are well known for their ability to nest in suburban and urban landscapes, making them a prime candidate for urban conservation. These small birds can also provide insight into the challenges urban cavity nesters face while raising young.

To study this particular species we have placed 20 artificial cavities (nest boxes) around Nature Boardwalk that we will be monitoring now through the end of the breeding season (late July). Since black-capped chickadees are much smaller than house sparrows, these nest boxes were designed to have a very small entry hole on the front that should allow chickadees to fit through while excluding the larger house sparrow.

One of the nest boxes, with part of the Chicago skyline in the background.

This study has just started at Nature Boardwalk, and it’s still too early to see nesting activity, but we are very excited to see if the chickadees will discover these new cavities. If you see any of the nest boxes, please observe them from a distance, as we don’t want to spook our new neighbors at the boardwalk!